An ab initio determination of 1A1-3B1 energy gap in CH2 using orthogonally spin-adapted state-universal and state-specific coupled-cluster methods

✍ Scribed by Piotr Piecuch; Xiangzhu Li; Josef Paldus

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 967 KB
• Volume: 230
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(94)01167-2

✦ Synopsis

The orthogonally spin-adapted open-shell state-universal (SU) and state-specific (SS) single and double coupled-cluster methods (CCSD) are applied to the singlet-triplet separation in methylene. Calculations have been performed using atomic-naturalorbital basis [ 5s4p3d2flg/3s2pid] and a few smaller basis sets. The best SS/SU CCSD result for the vibrationless 'AI-3B, separation ( YFpBo) using the nonrelativistic and Born-Oppenheimer approximations is 33 I5 cm -I. Accounting for the zeropoint energies, relativistic and diagonal Born-Oppenheimer corrections yield r,,= 3 184 or 3 133 cm-', in excellent agreement with the experimental values of 3 147 -fr 5,3 156 + 5 and 3 165 + 20 cm-'.